FileNotFoundException when using SPMetal

If you are working with SharePoint 2010 and using SPMetal to access list data in your site, you might encounter the error:

System.IO.FileNotFoundException: The Web application at [SITE] could not be found. Verify that you have typed the URL correctly
I created a code library project to include the SPMetal output file and do some business logic when accessing the SharePoint list data.

I want to test that code from Visual Studio, so I created a test project. Unfortunately the test projects run with the .net Framework 4 and you are not able to change that in the project properties.

So I used a console application with .net Framework 3.5 and I had to change the Target CPU to x64 (or you can use AnyCPU) because SharePoint is build only for 64 bit platforms.